Cadmium bright dip



Patented Apr. 1a. 1939 UNITED STATES PATENT OFFICE 6. Co p y. of Delaware Ldnrontdcleesnenrs Dei.,aoerpcratlen N'Dra A on! I "sdriaus'r scum. (cues-oi This invention relates to hydrogen peroslrh solutions which contain a nihstance of acid aaction and to their use as bright dips forcadmimn plated articles.

- The um plating processes now in use frequen product plated articles which are stained and which are not of a uniformly bright finish. With articles of very irregular shape some areas may be somevmat dull so that the piece does not have as uniformly a bright and lustrous finish as is desirable.

It has been proposed to dip the plated articles in solutions of dilute oxidizing acids, but while a fairly uniform finish is thus obtained, much of thecadmiumis dissolveda dtbeplating may be seriously damaged. If the solution of oxidising acidbediluteenoughnottoiniuretheplab.

ing. it is ineffective as a bright dip.

I have found that a hydrogen peroxide solu tion which contains a substance of acid reaction serves as a very satisfactory bright dip for cadmium plated articlca, My bright dip acts upon cadmium plated articles to give them a lustrous, uniformly bright finish free from stains g5 and discoloration.

Plated articles maybeleftinthe bath for a fairly long time without substantial damage to the plating. This offers a great advantage over the use of the previously proposed oxidizing acid so dips wherein the plating is dissolved with relativeiy great rapidity.

-One especiallybeneficlalefiectot mybright dips is that cadmium plated articles which have been brightened according to my invention subsequentlyshowareslstancetostainssuchasare produced by If a cadmium plated article which not been bright dipped is touchedbythefingerastainsareleftatthspclnts oi'contact. Itiaofcom'snverydifilcultto o handle such plated articles without injuring their finish. Articles which have been bright dipped according tomyinventionmaybohandledfreely without iniury to their finish.

Another advanta e of my bright dip is that the brightened platcnil-ybereadilyplated with other metals such as nickel. Prior to nickel platingiron orsteelitissometimes desirabietoplate the iron with cadmium, If the cadmimn plated iron orsteelisbrightdippedincertainosidising w acid dips. a subsequent nickel plate will not ad- 'here properly. .If the cadmium plated iron or steel is bright dipped in my bright dip. a subsequent nickel coat adheres in a very satisfactory Ihavealsofoundthatcadmitnnplated articles whichhave bemdippedin asolution ofacidified hydrogen peroxide are easily washed or rinsed ilter the dippin This is not true of some other oxidizing acid bright dips which form a colored film which requires considerable wash- 5 ing to efi'ect complete removal.

While an acidified hydrogen peroxide solution constitutes an excellent ls'ight dip. hydrogen peroxide in neutral or alkaline solution doa not have a satisfactory brightening action though 19 it may somethnes remove a slight amount of stain. Likewise, the acidifier alone may remove some stain but it does'not serve as a brightener in a satisfactory manner.

The following examples are given to explain is more fully the practice of my invention:

trample 14-h metal sheet bent to U-form was cadmium plated in a conventional manner. he use of a U-i'orm article closely approximates commercial plating conditions and the article is not '0 uniformly bright. being duller in the recessed portion. The plated article was rinsed free of the platingsolutionincoldwaterandthendipped for about fifteen seconds at room temperature in a brightdipconsistingof9ouncesofa30% (by weight) hydrogen peroxide solution, two-third of anounceofdd B6.0.P.sulfuricacidandagall0n of water. After removing the plated article from theln-ightdipitwascarefullywashedand dried. Theremltingplatedaheetbadalustromuniformly bright finish. the recessed portions being uniforminappcarancewiththerestofthearticle.

vI-prefertousea pureacidasimmrltiessuch asarecommonlyfoundinoommercial acids might cause decomposition of the peroxide. '5

The ratio of H102"?! weight) to HsSOe (by weight) is of great importance. In fact, it appearstobemoreimportantthantheperoxlde concentration. Astheacidisincreased andthe Biol/m ratio falls to one to one or below. the plate becomes white and as the ratio drops further becomes gray or black. The discolorationbythedip,wdtharatioofsubstantially belowonetoone.istyplcaiofadirectacidetch. This ratio is dependent to some extent upon the as actual concentration involved, a higher peroxide ratio being required in the more dilute solutions. For example, fair results were obtained using 2% HaBOnnd 2% 8s0rbyweight,but0.2% ofeach gavepoorresults. Goodbrightening canbeobgo tained, however, by using 0.5% H20] and 0.2% 8:80. lily preferred Bros/H2304 ratio is about four to one. with higher ratios the brightening action is more vigorous. but the stability of the dipisnotquiteasgreatand tbenostisincreased. g

action of a preliminary bath substantially free from oxidizing agents which comprises sulfuric acid, and exposing the cadmium to a bright dip which comprises hydrogen peroxide and sulfuric acid, the ratio of peroxide to acid in the bright 5 dip being no less than about four to one.

' RAYMOND J. KEPFEB. 

